I have tried in two cases.
Calling LogObject on a FMX TRectangle that is on the form, when clicking on a button on the form.
Creating the object in code and the trying to log it. Code snip :
if X > FNewCtrl.Position.X then
FNewCtrl.Width := X - FNewCtrl.Position.X;
if Y > FNewCtrl.Position.Y then
FNewCtrl.Height := Y - FNewCtrl.Position.Y;
A call to LogString below this code can access the Position X and Y.
tbsSiMain descends from TSiSession and has some additional methods, but does not override any existing methods.
Tracing through with the debugger, it is failing on this statement in SmartInspect.pas
AContext.EscapeItem(UnicodeString(LPropName)) + '=' +
with GetFloatProp(AInstance, LPropInfo) returning 0000000 for TRectangle StrokeThickness property.