Ya, 1K was easy for me to calculate 
Each virtualwrite will be about 5 bytes, plus data, which on a DHT11 may be around 2 bytes or so per sense (temp and Hum), so aprox 14+ bytes per data transmission. Plus 5 Bytes per heartbeat and keepalive?.. and who knows what else.
https://github.com/blynkkk/blynk-server/blob/master/docs/README_FOR_APP_DEVS.md#protocol-messages
Perhaps enable Debug and see what else might be going on.