Other stuff to keep in mind:

When a coffeemaker is listed as having a 12-cup capacity it's talking 6-friggin-ounce cups, which may be about 6 - 8 proper mugs. 12 tsp should get you a respectable brew.

When you pour the coffee, look to see if there's a wee spectral reflection on the surface, a bit like an oil-slick. This is the resin of the coffee bean coming out. It's a good thing and generally a sign of a well-brewed coffee.

Old timers swear swear by the act of adding a bit of ground eggshell in the brewing process as well.

Last resort: if - big if - the coffee is going to have to sit extra long, brewing it with a wee bit of salt will delay the onset of bitterness. I said a wee bit - you don't want a salt taste - maybe a dozen grains total.