Hiding Antenna in Fibreglass Chimnea?

Yes it likely will make a difference.

Self-built colinear antennas are notoriously unreliable in regards to performance.
I’d recommend trying to build this antenna: G7RGQ Antenna 1090MHz

Then the next question is which SDR you’re using.
The FA Pro+ (blue) is recommended and in some locations requires the additional FA filter.
Alternatively the rtl-sdr v3 with their rlt-sdr triple-filter LNA 1090 Mhz is a good combination.

Even this simple quarter wave antenna should be built as a simple reference design: QUICK SPIDER - No Soldering, No Connector
There is also a slightly better version near the end of the thread.