This has been a holy grail for many people for ages. The default stupid "FONT" with seemingly random sized text (0.152...), bottom left alignment has haunted us forever. I've never seen any solution, except to use a repeat region, which doesn't seem like a very nice way to go.
I suggest you to contact PTC Support and ask them to examine your problem.
PTC will tell you if it is "intended" functionality or a bug.
As far as I know, it can't be done. I've tried everything. You can edit the text style of the entire table at once, but if there isn't something in every cell (at least a space character), the formatting doesn't apply. Maybe create a product idea and post the link here.