I've been fiddling with T5's ship construction rules.

One thing I'm really liking is the TL adjusts on things.
It makes sense to me that you should be able to get things at a range
of size, cost, effectiveness, etc.

My question, though, is do the types "stack" ?

For example:
Power Plant-A is a TL9 thing.
If I build it as "Modified", then it is 2 TL's higher, a little
smaller, and half price.
So a TL-11 power plant would be half the price of a TL9 one, a little
smaller, a little more reliable. Makes sense.
You can build a TL9 plant as "Ultimate" , +4 TLs, and it's got much
more output, much smaller, more fuel efficient... and 4x normal price.
That kinda makes sense too : "We're taking every thing we know about
building these, and building the best we can, with cost as no object."
Such a power plant would be TL13.....

Which leads to my question:
Can one build a TL13 "Ultimate", then apply the +2TL "Modified" on it
to bump up to TL15?
Which would make it even smaller, more efficient, but best of all
change the price from x4 to x4/2 ?