I'm 99.9% sure you need the stand-offs. The p182 (from the picture) does not have raised spots for mobos, which would indicate that you definitely need them(plus..it comes with standoffs ). Try putting the mobo in at an angle (The I/O side in first) and getting them in and then screw down the opposite side. It's possible you might have to bend the board slightly (or the I/O panel)in that case, but hopefully(probably) not.
Use the standoffs that came with your case. It's quite possible however, that they are too long. There are half sized standoffs as well. It may be helpful to contact Anted customer support (they are good!) to see what they recommend.
Im using the I/O plate that came with my motherboard. I think there already is standoffs inside the chassi (it is 6+ raised spots inside and they are as long as the standoffs i got with my motherboard so i cant use both i think), and if not i have gotten the wrong standoffs with my motherboard because it raises the motherboard so that the I/O plate doesnt fit.