The 50 miles radius is what you've taken from the Q-header line.
The NOTAM simply says:
SOLENT CTA/SOUTHAMPTON CTR OPR HR MON-FRI 0530-2130 SAT 0530-2030 SUN 0630-2130
It only refers to the CTR in its normal geographical location. The 50 miles is only so that a narrow route briefing for anyone passing close to EGHI will pick up the NOTAM.
A human reader should never need to read the Q-line in order to get the full information content of the NOTAM.