I put three spikes and got the job done. No wobble. Rather than doing mods, maybe a "sharper spike" that goes through the carpet could be a solution.
With four spikes, you always have the problem of getting them to stabilize.... due to vibrations etc , you will find that you will need to tighten them occasionally. With three, you don't have that problem.
Stick to the original plans....... I have done it without any problems.
shreekant