How much does taking out the cushion lower you? I'd bet the seat just has a beefy cushion.

 

Last time I pulled my cushon I burned my butt. Did not like...

 

Here's a pic of what I did.

 

ok from the pictures the side mounts look like the issue. usually the side mounts are not oriented like that. that are set on the angle iron the long way. perhaps that will get you lower. if that doesnt help I would just set the seat on the floor raise the front like a inch or as much as you can/want and take some measurements and make some new holes.