Toilet flange is too high above concrete floor.

steel flange?

You cant glue steel. Maybe jb weld but that's another story.

Cut it out from the inside, glue coupling and cut half an inch off. Done.

Find a toilet that has more space, or tile around the "throne" area.

Why do you have to deal with all 5 toilets?

I need to replace all toilets with 1.6 gal toilets for resale purposes. Two of them are cracked.

All toilets, at least the ones I looked at, have the same recess. Just enough to allow for a 1/4" flange above the floor level plus a wax ring. Maybe I should look some more.

Borg may not have them, but a real plumbing house probably has purpose-built shims to put under toilet to raise it up, that match the countour for the brand you need. If you are willing to spend the time, you could probably get 5 scraps of solid-surface material from a kitchen place, and carve your own with drill and jigsaw. Just make a cardboard template to lay it out, and mark where to cut and drill. With a good template, the kitchen place may even be willing to do the carving pretty cheaply for you.

If it ain't one thing, it's another.

Lay out some nice ceramic tile under and round the toilets.

Where do you live that they demand you put low flush toilets in, Kaliforia?

Many toilet flanges are thicker than 1/4". I just measured the Oatey like the one I used and it is 3/8" and worked fine. The recess in the bottom of the toilet does vary by manufacturer but are you sure you are measuring correctly? The wax compresses as much as needed, there is virtually no height needed. If you cannot locate one that will fit a 1/2" flange you can install a toilet floor plate. This company makes nice ones, although they are almost $50.

-- DT

Why does anyone NEED 5 toilets? The OP must be full of s*it to need that many toilets.

That's exactly what I was thinking. Some type of fake marble or stone countertop shaped to fit. Get all 5 toilets the same so you only have 1 template and it should get cheaper if they make all 5 the same.