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 u in range(int(input())):
    n=int(input())
    l=list(map(int,input().split()))
    x=-1
    m=max(l)
    if(len(set(l))==1):
        print(-1)
    elif(l[0]==m and l[0]>l[1]):
        x=1
        print(1)
    elif(l[n-1]==m and l[n-1]>l[n-2]):
        print(n)
    else:
        for i in range(1,n-1):
            if(l[i]>l[i-1] and l[i]==m):
                x=i+1
                break
            elif(l[i]>l[i+1] and l[i]==m):
                x=i+1
                break
        print(x)
