Any Agricultural Trade Officer and the senior representative of the Secretary of Agriculture assigned to a nation under subchapter I of this chapter may, under regulations prescribed by the Secretary of Agriculture, be entitled to receive a representation allowance in an amount determined by considering (1) the extent to which such Agricultural Trade Officer or senior representative can effectively use such funds to further the purposes of this chapter, (2) travel and entertainment expenses customary in the private trade for persons of comparable rank and salary, and (3) customs and practices in the nation where such Agricultural Trade Officer or senior representative is assigned.