Well, it wont be hard to turn if the injector is out because there will be no compression, but it is true that both valve rockers will have slight clearance at TDC Compression stroke, if the valves are adjusted properly.
If you can find the point at which your probe wire stops rising (exactly stops) and then the point at which it begins to descend again, and then split the difference between those two points, you will be exactly at TDC.