a) put at window area (maybe put a table there) , facing out to the sky w/o blocking, don't put behind wall again.

b) or if u got useless camera tripod, also can use it to mount the antenna with anti-slip mat, and put the tripod near window, with that kind setup u can easily do antenna angle adjustment and even relocate tripod with antenna anytime u like, it is full of variety setup way... endless imagination (while got time i shoot a picture of sample)

i suggest (b) as angle adjustment very helpful at your scenario as u r at 17th floor to get desired result.