gekko doesn't trade the whole amount

[crypt0r]

hi,

everything works fine for me so far 

but i have just a question because my gekko doesnt use the whole amount of currency or asset.

for example i have 1000usd and gekko buys xrp but not for the whole 1000usd, so there is always 35-40usd rest.
or when selling back from xrp to usd gekko doesn't sell all xrp, so like about 90 xrp will stay.

is this maybe misconfiguration by me or it is like some security margin so gekko can be sure the amount is big enough so the order will not be canceled or something? 

thanks