I think it is more time frame. I recall GMST talking about using their sash tied to their feet to do upside down situps.
Master Ie is never in a gi but I have seen Master Hiang in a gi in a painting with Master Ie . What time frame was the trouble in Indonesia? Late 50s and early 60s? I think that would be the time frame that they would have started using them. But just guessing.
Master Sin said that Master Ie was of slight built.
That one photo looks like Master Hiang.