Morgan, I'm not loving that oven dimension (~15" square), but, if that's what you've got, we'll make it work.
I wouldn't normally ask this, but, because your oven is so small, is there any chance you know that wattage of your oven? Do you have a brand and model #?
Does this oven have a convection fan feature?
Could you list the ingredients for the hiivaleipäjauho? From what I've read on Finnish flour, 14% feels a little high.
Also, could you take a photo of the broiler in the top of your oven?