The difference appears to be that a pad lookup requires a single opcode where dereferencing a hashref requires three opcodes:

9     <;> nextstate(main 47 -e:1) v:%,{ ->a                   f     <;
+> nextstate(main 47 -e:1) v:%,{ ->g
a     <;> nextstate(main 47 -e:1) v:%,{ ->b                   g     <;
+> nextstate(main 47 -e:1) v:%,{ ->h
m     <2> leaveloop vK/2 ->n                                  u     <2
+> leaveloop vK/2 ->v
f        <{> enteriter(next->j last->m redo->g) lKS/8 ->k     l       
+ <{> enteriter(next->r last->u redo->m) lKS/8 ->s
-           <0> ex-pushmark s ->b                             -       
+    <0> ex-pushmark s ->h
-           <1> ex-list lK ->e                                -       
+    <1> ex-list lK ->k
b              <0> pushmark s ->c                             h       
+       <0> pushmark s ->i
c              <$> const[IV 1] s ->d                          i       
+       <$> const[IV 1] s ->j
d              <$> const[IV 10] s ->e                         j       
+       <$> const[IV 10] s ->k
e           <#> gv[*_] s ->f                                  k       
+    <#> gv[*_] s ->l
-        <1> null vK/1 ->m                                    -       
+ <1> null vK/1 ->u
l           <|> and(other->g) vK/1 ->m                        t       
+    <|> and(other->m) vK/1 ->u
k              <0> iter s ->l                                 s       
+       <0> iter s ->t
-              <@> lineseq vK ->-                             -       
+       <@> lineseq vK ->-
i                 <1> exists vK/1 ->j                         q       
+          <1> exists vK/1 ->r
-                    <1> ex-helem sK/2 ->i                    -       
+             <1> ex-helem sK/2 ->q
g                       <0> padhv[%h:46,47] sR ->h            o       
+                <1> rv2hv[t8] sKR/1 ->p
                                                              n       
+                   <1> rv2sv sKM/DREFHV,1 ->o
                                                              m       
+                      <#> gv[*r] s ->n
-                       <1> ex-rv2sv sK/1 ->-                 -       
+                <1> ex-rv2sv sK/1 ->-
h                          <#> gvsv[*_] s ->i                 p       
+                   <#> gvsv[*_] s ->q
j                 <0> unstack v ->k                           r       
+          <0> unstack v ->s
-e syntax OK                                                  -e synta
+x OK
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I made a mistake (used a global reference); the difference is one extra opcode, not two extra:

9     <;> nextstate(main 47 -e:1) v:%,{ ->a               f     <;> ne
+xtstate(main 48 -e:1) v:%,{ ->g
a     <;> nextstate(main 47 -e:1) v:%,{ ->b               g     <;> ne
+xtstate(main 48 -e:1) v:%,{ ->h
m     <2> leaveloop vK/2 ->n                              t     <2> le
+aveloop vK/2 ->u
f        <{> enteriter(next->j last->m redo->g) lKS/8 ->k l        <{>
+ enteriter(next->q last->t redo->m) lKS/8 ->r
-           <0> ex-pushmark s ->b                         -           
+<0> ex-pushmark s ->h
-           <1> ex-list lK ->e                            -           
+<1> ex-list lK ->k
b              <0> pushmark s ->c                         h           
+   <0> pushmark s ->i
c              <$> const[IV 1] s ->d                      i           
+   <$> const[IV 1] s ->j
d              <$> const[IV 10] s ->e                     j           
+   <$> const[IV 10] s ->k
e           <#> gv[*_] s ->f                              k           
+<#> gv[*_] s ->l
-        <1> null vK/1 ->m                                -        <1>
+ null vK/1 ->t
l           <|> and(other->g) vK/1 ->m                    s           
+<|> and(other->m) vK/1 ->t
k              <0> iter s ->l                             r           
+   <0> iter s ->s
-              <@> lineseq vK ->-                         -           
+   <@> lineseq vK ->-
i                 <1> exists vK/1 ->j                     p           
+      <1> exists vK/1 ->q
-                    <1> ex-helem sK/2 ->i                -           
+         <1> ex-helem sK/2 ->p
                                                          n           
+            <1> rv2hv[t7] sKR/1 ->o
g                       <0> padhv[%h:46,47] sR ->h        m           
+               <0> padsv[$r:47,48] sM/DREFHV ->n
-                       <1> ex-rv2sv sK/1 ->-             -           
+            <1> ex-rv2sv sK/1 ->-
h                          <#> gvsv[*_] s ->i             o           
+               <#> gvsv[*_] s ->p
j                 <0> unstack v ->k                       q           
+      <0> unstack v ->r
-e syntax OK                                              e syntax OK
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