as I said earlier it's a visualization thing for me really. But don't forget that Berowyn's shield is by FAR the most effective one we ever see, in fact we know from an Aes Sedai perspective that she should not be able to hold a woman anywhere near to Nynaeve's strength ... which implies that the shields normally taught to Aes Sedai are rigid and not flexible and only work on women very close to your own strength. Galina notes that she could easily break Micarra's shield, who is 13 levels lower than Galina, meanwhile Berowyn is 38 levels below Nynaeve (3x the difference) and easily contains her, I wonder if she could hold a man equal to Nynaeve.

I suspect Aes Sedai shielding was "innovated" by the Red and was primarily used for shielding men. It goes, at least thematically, that most female centric channeling organizations would also have developed shielding methods more suited to holding men than women given the situation with the Taint.

saidar is a force that requires passive direction not manhandling, saidin is a force that requires aggressive maneuvering rather than guidance. The way I see an effective shield for saidar is the way Berowyn struck upon it, something flexible, meant to contain a heavy volume of liquid. The way I see an effective shield for saidin is more of an immovable object meant to stop bullets (i.e. bulletproof glass or if you wish to stay with the water theme, an umbrella stopping rain)

I do agree with you that the opposing natures of saidin and saidar probably play a role in this as well and likely enhances the difficulty with shields on the opposite sex.