No, that is not what you said. You used the word sizeable, and were not willing to justify what you meant by it.
You stated that a "sizeable" number of mosques were radicalising muslims. Sizeable means "of considerable size". You didn't clarify what you meant by that, and you still haven't.
I still contend that you are making it up, and without any evidence from your end, you simply cannot refute that.
'Considerable size' will do me fine.
What you seem to want is some kind of accurate statistic like 38.2% of mosques are involved in radicalising muslims. However nobody keeps stats like that hence "sizeable".