The Shield building rules state it as being bought as a multipower with 2 slots. The second slot being the 'Bash' slot. It has a limitation on it that sets an OCV penalty as equal to the DCV to simulate a large shield is unwieldly and hard to 'bash' with (Fantasy Hero page 198).
The underlying principle in Hero is there is no ONE right way to build anything. In fact the flexibility means there are numerous equally right ways to do EVERYTHING. That is what makes it the system par excellance!
If you want more bash in your shields, drop the OCV penalty. Or drop the off hand penalty. Or you can assign a surprise bonus for the attack. Or if you really want to simulate bashes as being easy use the DCV modifier as an OCV bonus for bashes. Do any or all of the above. Its your game, or your GM's, and you should do what makes the most sense to you. If everyone is having fun and everyone agrees then the rule works, if not make it so it does.
The difference between game designers and us, is practice and a paycheck