Hi,
Because HikaShop can display products from a category and his sub categories, the sorting can look non consistent.
You can put the numbers you want, if there are several times the same number it won't generate a bug, the products will have the same "ordering" and the product id will be use to make the "difference" between them.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.