1
3
5 3 4
 6
5
5 3 4 4 5
3
1 1 1
5
4 4 3 4 4
5
5 5 4 3 2
3
1 1 2
5
5 4 3 5 5
 1
3
10 1 5

1
 1
-1
2
2
3
1
 1


for _ in range(int(input())):
    n = int(input())
    list_s = list(map(int, input().split()))
    
    if(len(set(list_s))==1):
        print(-1)
        continue
    
    maxEle = max(list_s)
    switch = 0
    for i in range(n-1):
        if(list_s[i]==maxEle and list_s[i+1] < maxEle):
            print(i+1)
            switch = 1
            break
        
    if(switch==0):
        for i in range(1,n):
            if(list_s[i]==maxEle and list_s[i-1] < maxEle):
                print(i+1)
                break
    
    