hmm I thought the sidebar width the inner width being around... 230 pixels
with the margins (inner and outer + thumb margins) you could have a maximum of 52 pixels thumbnail size.. otherwise the layout would break.
But anyway I fear it is not possible without creating a new imagebit template.
and modifying the code so that it would use it.
The problem is as there are not Tables on forum home, everybody was asking NOT to use tables for gallery at least not on forum home!!!. (the page would not render before tables are completely rendered, and there are seo
problems with tables as the content is not a table content)
So that would mean completely new css and template and code for that page.
and your whole site would have to use 52px thumbnails at a maximum.
(with 2 in a row you could use 75px)
So for the moment, sorry its not on the priority list (its really lots of work)