What size do April Tags need to be?

I created a project.  I went to Tools and saw that April tags need to be at least 35x35 pixels.  If I am flying a job with a Phantom 4 RTK at an altitude of 71m AGL that gives me a GSD if 1.95 cm/px  If we calculate that out to 35px by 35px that gives us a target size of at LEAST 28"x28".  I use the 71m AGL so that according to Bentley I should be getting an accuracy of +/- 0.20' vertical for my meshes.  (That is 3x the GSD.)  We had planned on printing out about a dozen or so of these to have as permanent targets that we could take from site to site and have quick control points.

Having to print these onto a piece of media that is about 30"x30" makes this process a LOT less desirable.  Is there anything we can do to bring that size down some or is 35x35px the minimum?