i've been reading the ER datasheet and the previous posts. here are some comments and ideas that might be able to start some new discussion.
i'm assuming here you're using the ERx00TRS modules. these are the transceiver variety, and hopefully the 2nd generation version. i'm assuming you are communicating to your ER enabled robot/system with, obviously, an ER enable PC. the ER might be connected to a USB-RS232 converter or a dedicated RS232 on your PC. i also assume that the software that you are using to transfer/download the "application" is FBOOT17.EXE. wheew too many assumptions!
all page references refer to the ER data sheet.
1) on page 12, End of Data Delay, is your code implementing this delay?
i don't think the downloader you are using knows this, so it might just be streaming data continuously. this would work if your wired since the connection is more stable, ie less erroneous packets, and you have no transfer overhead!
for an ER radio connection, according to page 12, there's a 13.2ms of overhead for each packet (this occurs even if you just transfer one character) so for example you are streaming data, the buffer gets full and the ER transmit, but while transmitting (before the 13.2ms is over!) you begin writing to the ER again, you risk destroying the data in the buffer that is currently being transmitted.
2) on page 12, Buffer Size, i hope you're buffering or sending your data in chunks/blocks that are 180-bytes or less in length.
i assume the 180 buffer is used for both Tx and Rx, since the ER is half-duplex only and there are those warnings of buffer corruption strewn all over the ER's data sheet.
do you still remember the UART_TX_BUFFER_SIZE that you posted? maybe you can try increasing that to 128 to closely match the ER's buffer size.
3) the ER is only half-duplex!
did i mentioned this already? you risk destroying the contents of the receive buffers if you try to send anything through the air while the ER is still receiving (again, based on the data sheet).
4) use Busy Output (CTS) and Host Ready Input (RTS) pins on the ER, as you've mentioned
this will be additional coding and probably additional traces/wires on your board. this could be extra work but incorporating CTS/RTS to your solution to 1 and 2 above is the best solution.
understanding 1, 2, 3 above is very important. If you continuously stream data over the air without the End of Data Delay, you'll be writing over the ER's buffers which will cause loss of data. blocking the data you are sending will also maximize the throughput of your ER since you will be trying to use up most of ER's 180-byte buffer before transmitting, and minimizing the overhead caused by the transmission delay. but everything will be in vain if 4 is not implemented.
try to find the "Easy-Radio Software Guide" mentioned in the data sheet, it might be helpful.
btw, a disclaimer, i don't have any actual experience working with the ER! so all this assumptions and theories could be totally rubbish
Seriously, I hope this helps!