Installing ceiling boots (basement hvac)

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.
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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
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