ML Dynamo 700 Subwoofer - Fwd or Down?

I have a Martin Logan Dynamo 700 subwoofer that has more power than my house can handle. I've had it setup in the bottom firing configuration and it sounds great, but when watching movies with extreme bass it will actually move around on the laminate floor and even vibrate the laminate on the subfloor. I tried using the spikes and it actually made the vibration worse. I have the option to set it up in a forward firing configuration and did it tonight (I've done for a short time before). Is there really any significant advantage of one over the other? I've seen many quality subwoofer designed both ways.