Call costs clarifications.

gas.md

@@ -472,6 +472,15 @@ now we can "hide" this cost in the codeLoadingCost/codeByteLoadingCost values,
 and we'll make the error case less efficient.
 TODO: Clarify codeLoadingCost/codeByteLoadingCost.
 
+Although the caller pays for code loading one way or another, one may argue
+that this should be paid from the `GCAP`. However, it seems conceptually easier
+to consider that `GCAP` pays for the running cost of the contract, so it will
+not include the code loading cost.
+
+Also, it may seem counterintuitive to pay for the code loading cost, one may
+expect to pay a flat fee as in the EVM model. A flat fee is usually less
+efficient, so we're using a size-based fee.
+
   ```hs
   -- CALLOP in [CALL, CALLCODE, DELEGATECALL, STATICCALL]
 
@@ -515,6 +524,8 @@ TODO: CALL loads some data in `<callData>`, but that's not used anywhere.
       Above I included a possible definition (`callDataSetupCost`), but we
       should find out what happens to that and include the right cost.
 
+TODO: Is the callFeeCost fixed or based on the stack size?
+
 TODO: Returning can be either implicit or explicit, should take that into
       account