minmum separation between the wearable antenna and body

how to calculate the minimum separation between body and wearable antennas. if it's very small the absorption because of body will be high and and also it effects the input impedance and the radiation pattern of the antenna.
one good approximation is to be keep the distance of (2d2/lambda) from the body for which results are close to a free space response. (all these got from the journals).

can someone tell whether these are correct or not. also what options are there to improve the performance of the antenna in opposite to body direction and keeping the distance minimum from body.(basically min radiation towards the body)

Yes, 2D2/λ it's a good starting point.

case 1 - is this will be enough, because the patch antenna i am using is supposed to radiate almost same in all direction(omnidirectional kind of pattern),

case 2 - also what if i want to improve the performance only in the opposite to body direction (min direction on body side)?

because since the dielectric of body is much higher than free space the fields will be more dense on body side. so on moving away from body the effective dielectric decreases on the body side and hence better radiation(for omnidirectional pattern). don't know about how the pattern will be for directional case



also this minimum distance works for chip antenna as well, or it's to be used for printed antenna only.