I advise you to to the transition just after that you have sent the dividends for the following reasons.
1-If someone buy asset CNYcoine @ 1 CNY, then early investors and you are screwed (NAV decrease).
I agree with you at this position. This is not fair.
2-If someone buy asset CNYcoine @ 1.194 CNY (value with investor profits), then the NAV will decrease so early investors are screwed.
But I don't agree with you at this stage. it's fair and no change in NAV and no screw for non of new investors and early investors. I think if we remove Coinex half benefit from NAV, then the NAV will not change by new investors joint.
3-If someone buy asset CNY coine @ 1.389 CNY, then NAV will not change but more shares are issued, you will get more profits (50%) but the new investors are screwed (which is acceptable at the beginigs of the month but not few day before dividends.
I agree also that this is not fair. And this was the mistake I made for the last 6 Asset sold and then changed to 6.58.
So for three options above I think that option 1 and 3 are not fair but option 2 is fair(I added numbers) and we plan to accept new investors with that option before and after first day of each month.
Let me know if I missed something or you think I'm wrong, please. 
Thanks,
Sepehr
Why option 2 is not fair:
Total asset value = NAV * number of assets
so NAV = Total asset value / number of asset
Investor profit = number of asset hold * (NAV end month - NAV beg of month) * 50%
Let say there is 1000 asset (NAV currently at 1.39)
If one investor buy 1000 shares at 1.19, NAV will be at 1.29 but more shares will be emmitted , but on early investor side the NAV has decreased and they have the same number of shares, so they loose profit...
Case 1 (without new investor) : 1000*(1.39-1)*0.5 = 195 of profit (195 for you as well)
Case2 (with new investot @ 1.19) : 1000*(1.29-1)*0.5= 145 of profit (290 for you as there is twice more shares)
New investor should join at the begining of the month or later at NAV price but at their own risk.
When an investor want to leave the asset he leaves either at price of the begining of the month or directly on the AE.
If you want investor can join the asset more often you should make weekly dividends.