How change float to byte[] and then byte[] to float without accuracy lost?

I use google play game services for unity.
Send packet look like this:

byte mPosPacket = new byte[4];

public void BroadCastPosition() {

mPosPacket[0] = (byte) 'P';
mPosPacket [1] = (byte)position.x;
mPosPacket [2] = (byte)position.y;
mPosPacket [3] = (byte)position.z;
    PlayGamesPlatform.Instance.RealTime.SendMessageToAll(false, mPosPacket);
}

Recive look like this:

public void OnRealTimeMessageReceived(bool isReliable, string senderId, byte data) {

	if (data [0] == (byte)'P') {
		posX = (float)data [1];
		posY = (float)data [2];
		posZ = (float)data [3];
	}

With this everything work but for example when send float 2.4243, recive float 2. I need more accurate.
When I use System.bitconverter float is super accurate but i can’t give something like this “mPosPacket[0] = (byte) ‘P’;”
Anyone know way to recognize byte or use bitconverter to start with 1 index?

I need something like this:

mPosPacket[0] = (byte) ‘P’;

mPosPacket[1], mPosPacket[2], mPosPacket[3] is one float

Use DataStream to convert primitive types to their byte repesentations and back

Edit:
Actually in c# you use BinaryWriter, my mistake. Its the same basic thing though

float f = 3.1415;
MemoryStream stream = new MemoryStream();
BinaryWriter bw = new BinaryWriter(stream);
bw.Write(f);
bw.Flush();
byte[] floatBytes = stream.ToArray();

Do the reverse with BinaryReader to convert back.

Note that, rather then doing this for each float, you can create one stream that has all your data in it with successive writes and get it back with successive reads.