Problem with vacuity install?

I'm trying to install a vacuity toilet. On the back of the bowl there is a raised "bar", such that the tank, when tightened down completely, is not level. It leans forward.

If I can manage to insert this image, here is what it looks like from the side:
https://terrylove.com/forums/attachment.php?attachmentid=356&stc=1

The tank is already resting on the "bar" even before tightening:
https://terrylove.com/forums/attachment.php?attachmentid=357&stc=1

Here's the bottom of the tank:


When I tighten the tank bolts, the larger foam seal gets compressed and I've got the leaning toilet of Pisa. If I don't tighten it that much, it leaks. Any suggestions? I've been thinking of trying to grind down the bar on the back of the bowl a few mm, but I'm not sure how to (or if I can) do that.

Thanks a bunch!

How straight is it when it's fully tightened down?

I would say it is 5-8 degrees. It is enough that it is obviously leaning out from the wall when installed. But it isn't so bad that the seat won't stay up.

Thanks again for your advice.

I have installed a number of these toilets and found that I could tighten the bolts enough to make the entire tank level and this compressed and sealed the gaskets sufficiently. I suspect Briggs designed the lip to keep us from cranking down the seals too far!