I am working on basement mechanicals

I need to install 6 hvac boots, 5 - 12x4 x 6" and one 4"... and few
wyes8x6x6

All joist installed with 24" span .

I intend to rivet 2L shaped tin pcs something like 7x1 and attached it
to each
side of the boot. Should I offset those ears, by 1/2" like outlet
boxes?

Thanks.

Hard to understand your question ...but the boots should mounted so
that they will extend into the sheetrock that will be later added...1/2
to 5/8 inch below the joist or truss